1. Field of the Invention
The present invention relates to a sound effect circuit and processing method for providing sound effects to a digital audio signal using a pulse code modulation (PCM) scheme or the like
2. Description of the Related Art
A sound effect circuit that provides various sound effects to a digital audio signal is well known to those skilled in the art. In this sound effect circuit, for example, a feedback circuit such as an infinite impulse response (IIR) filter may be used as a band pass filter which divides an input sound into a high-pitched tone, middle-pitched tone and low-pitched tone. However, in this feedback circuit, there is a problem that some limit cycle oscillation noise significantly occur when the level of an input audio signal is close to a silence state. As a means for settling this problem may be considered a method that internally converts the number of quantized bits of an input audio signal, for example, 16 bits into 24 bits and performs a 24-bit operation to realize a sound effect function. However, this method has a disadvantage of increasing a circuit scale.
On the other hand, as a method or apparatus for reducing unpleasantness given to a viewer due to noise in the silence state, Japanese Patent Laid-open Publication No. 2005-079877 discloses a configuration that mutes the output of audio data when the level of a clock supplied together with the audio data is lower than a threshold value. Also, Japanese Patent Laid-open Publication No. 2006-279194 discloses a configuration that commences fade-out when the output level of an audio signal is lower than a threshold value for a certain period and subsequently performs muting when the output level of the audio signal is lower than a threshold value for a certain period.